1. Field of the Invention
The present invention relates to: an image processing method and an image processing device enabling faithful reproduction of appearance and further preferred color reproduction of appearance, for reproducing a subject image such as a subject image obtained directly by photographing a subject or from a color negative film or a displayed transparent image on a color reversal film (hereinafter, also simply referred to as a transparent image) on a color photo print (hereinafter, also simply referred to as a print) as a hardcopy image (a reflection image or a print image) and/or on a display screen (a monitor) as a softcopy image (a monitor display image); an image output device (an image forming device) and a digital camera using the image processing method and device; an image processing program for executing the image processing method; and a recording medium on which the image processing program is recorded.
More specifically, the present invention relates to: an image processing method and an image processing device enabling faithful reproduction of appearance of the above-mentioned subject image such as a subject or a displayed transparent image when the subject image (the subject or the displayed transparent image) is output to a display medium such as a print or a monitor display screen as a reproduced image and, in addition, enabling conversion for obtaining preferred color reproduction; an image output device (an image forming device) and a digital camera using the image processing method and device; an image processing program for executing the image processing method; and a recording medium on which the image processing program is recorded.
In particular, the present invention relates to: an image processing method and an image processing device enabling color conversion for faithfully reproducing the appearance of a subject image such as a subject or a displayed transparent image, and in addition, enabling color conversion to values (lightness and chroma) for achieving preferred color reproduction common to various subjects and scenes, that is, executing a color conversion method for creating a reproduced image such as a color print or a monitor image; an image output device (an image forming device) using the image processing method and device; an image processing program for executing the image processing method; and a recording medium on which the image processing program is recorded.
Throughout this specification, the term “subject” encompasses all objects to be photographed, which are present in a photographed scene by a digital camera or on a color negative film or a color reversal film (that is, not limited to a main subject such as a person and denotes the entire scene including the background). The term “appearance” of an image denotes a kind of subjective evaluation by multiple observers, and serves as an evaluation index of the appearance of a subject image (a photographed subject by a digital camera or on a color negative film and a displayed transparent image on a color reversal film) by multiple observers under an actual viewing condition.
2. Prior Art
In the technical field of photography, how to reproduce a subject (a photographed scene) on a print has been discussed since a long time ago. Although a unified answer for this question can hardly be found because the answer may differ depending on the contents of a subject, photographic conditions, or the regions and cultures. In the basic idea of photography, however, the reproduction closer to the visual impression of a human being (observer) when he/she sees a subject is preferred.
For example, from the above-described point of view, JP 6-139323 A discloses a method involving digitalizing an image photographed on a color negative film, obtaining colorimetric information of a subject by digital signal processing, and then reproducing calorimetric values on a print. According to the patent publication 1, by directly reproducing the obtained calorimetric values on a print, it is possible to faithfully reproduce the calorimetric values of a subject.
On the other hand, a transparent image on a color reversal film is capable of offering a vivid color which is lit up by high-luminance light from a projector or a viewer and is also capable of producing subtle shades of color or a wide range of colors. Therefore, the transparent image is mainly viewed on a projector, a viewer, or the like.
A transparent image on a color reversal film is also reproduced to be viewed as a photo print (a reflection image or a hardcopy image) similarly to a photographed image on a color negative film.
As described above, since the color reversal film is capable of offering a wide range of colors such as vivid colors lit up by light and subtle shades of color as compared with the color negative film, prints produced from the color reversal film is used by professional photographers, photography experts (high-level amateurs), and the like. In the current situation, however, general users use the prints obtained from the color reversal film less frequently than the prints produced from the color negative film.
In view of such a situation, there exists a digital photo printer capable of digitally processing and outputting not only an image photographed on a color negative film but also an image photographed on a color reversal film. However, since there is a request for reproduction of subtle shades of color or a wide range of colors on a print from a color reversal film, the existence of an optical print (analog print), which is obtained by direct printing from a color reversal film, is absolute. For this reason, a print superior to the optical print has not been developed until now. Therefore, the color reproduction unique to the transparent image on the color reversal film is not fully taken into consideration in the digital photo printer. The finish of a print from a transparent image on the color reversal film exclusively depends on the performance of a print photographic sensitive material in the actual situation.
Moreover, in recent years, there is a request for color reproduction with a high chroma also in an optical print with the increased chroma of a color reversal film.
In comparison of a print produced according to the method described in JP 6-139323 A and an original photographed scene (that is, a subject) with each other, the produced print sometimes practically fails to reproduce the appearance of the photographed scene. Similarly, in the case of a color reversal film, the produced print sometimes fails to reproduce the appearance of a transparent image to be viewed.
Furthermore, a user produces a photo print by reproducing a transparent image on a color reversal film after he/she views the transparent image with a projector, a viewer, or the like. Specifically, when a print is to be produced from a color reversal film, the user more frequently expects that the appearance of a transparent image on the color reversal film, which has been viewed with a projector, a viewer, or the like, is reproduced on the print, rather than the appearance of a subject image when a subject is photographed on the color reversal film.
However, the photo prints produced based on the transparent images on the color reversal films which are now sold in the market do not faithfully reproduce the color gradation of the originals of the transparent images to be viewed or “bright beauty”, which is one of the characteristics of color reproduction. Therefore, there is a problem in that the user who expects the reproduction of finesse of the original of a transparent image on a print cannot be fully satisfied. Specifically, the print produced based on a transparent image on a color reversal film is not produced by an image processing method for providing the reproduction close to the visual impression that a human being (observer) has when he/she sees the transparent image, and therefore has a problem in that its finish depends on the performance of the photographic sensitive material of a print.
For the above-described reason, in the field of photo print production such as in a laboratory, in order to achieve a match in appearance between a transparent image on a color reversal film viewed with a viewer or the like and a print, an operator displays digital image data read by a scanner such as a digital photo printer from an image on a color reversal film on a display or the like in which the matching between a printer output and the corresponding color is achieved, and also observes the transparent image on the color reversal film displayed on the viewer so as to manually adjust the digital image data for matching between the appearance of the display image on the display, which is color adjusted with a hardcopy printer for output, and the appearance of the transparent image. However, the adjustment is not only extremely difficult but also extremely troublesome. In the case of an inexperienced operator, in particular, there is a problem in that expected results cannot always be obtained.